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How does EF4 compare with NHibernate?

This is better? I heard the CodeFirst extension, but it's ready for prime time. Share your experience with development, any performance overhead, etc.

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entity-framework nhibernate entity-framework-4 fluent-nhibernate entity-framework-ctp5
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I think this is a timely question, since I was interested in the same thing. I am trying to create a serious model of e-commerce, and I am trying to get my POCOs to get rid of persistence problems and also try to stay true to Domain Driven Design. So far, I am very careful, and I am on the fence about whether I should jump from a ship in NHibernate. The only thing that keeps me from doing this is that I assume that Microsoft will improve (and quickly).

Some of the biggest problems so far are:

  • Inability to precisely control the materialization of an object. EF calls the zero-arg constructor on your POCO, and you cannot change this behavior.
  • No enumeration support. The community screamed - screamed! - for this, and this did not happen. Workarounds are terrible and pollute your domain model.
  • Strange display errors when trying to manage column names and relationships in a database. The main ones that I can think of are complex keys and many-to-many relationships. They can be circumvented, and I assume that they will be fixed by the time of release, but nevertheless they disappoint.
  • Bad SQL. I also work with DBA, and the SQL that generates EF (with or without Code-First) is terrible.

And that’s just the tip of the iceberg: I’m just starting to learn EF4, and I’m running into terrible roadblocks. As I think of other reasons, I will add them here. I'm still fighting for it.

(I wonder if the community will give another vote “without confidence.”)

More details:

  • To add to the problem of “Weird mapping bugs”: you cannot control the column name if it is involved in self-reference (for example, if you have a hierarchy). I assume this will be fixed in the final version.
  • Lack of batch processing, which leads to many database calls. For example, how do you delete a bunch of items from a collection? Load all objects into memory and delete them one at a time. A smaller problem is the number of database accesses when pasted into tables that are involved in relation to inheritance.
  • There is no reasonable way to deal with model changes. EF Code-First loves to completely drop your entire database if you need to change the schema.
  • Multiple extensibility points. You can literally count, on the one hand, the number of events that EF4 allows you to subscribe to (and Code-First does not provide much more).
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As for me - I prefer EF, but with some improvements. Basically, EF offers you the following benefits:

  • Visual model editor
  • Database / Model Update Wizard (instead of manual XML changes - which is terrible for me)

In addition, I use 3-party commercial tools based on EF and L2S ( LinqConnect ), which provide me with the following features:

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